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See Inside March 2009

Does Daylight Saving Time Conserve Energy?

Recent studies shed some light on the efficiency of seasonally changing the clocks



© ISTOCKPHOTO / KIYOSHI TAKAHASE SEGUNDO

Starting this month, roughly one quarter of the world’s population will lose sleep and gain sunlight as they set their clocks ahead for daylight saving. People may think that with the time shift, they are conserving electricity otherwise spent on lighting. But recent studies have cast doubt on the energy argument—some research has even found that it ultimately leads to greater power use.

Benjamin Franklin is credited with conceiving the idea of daylight saving in 1784 to conserve candles, but the U.S. did not institute it until World War I as a way to preserve resources for the war effort. The first comprehensive study of its effectiveness occurred during the oil crisis of the 1970s, when the U.S. Department of Transportation found that daylight saving trimmed national electricity usage by roughly 1 percent compared with standard time.

Scant research had been done since, during which time U.S. electricity usage patterns have changed as air conditioning and household electronics have become more pervasive, observes economist Matthew Kotchen of the University of California, Santa Barbara. But lately, changes to daylight saving policies on state and federal levels have presented investigators new chances to explore the before-and-after impacts of the clock shift.

In 2006 Indiana instituted daylight saving statewide for the first time. (Before then, daylight time confusingly was in effect in just a handful of Indiana’s counties.) Examining electricity usage and billing since the statewide change, Kotchen and his colleague Laura Grant unexpectedly found that daylight time led to a 1 percent overall rise in residential electricity use, costing the state an extra $9 million. Although daylight time reduces demand for household lighting, the researchers suggest that it increased demand for cooling on summer evenings and heating in early spring and late fall mornings. They hope to publish their conclusions this year in the Quarterly Journal of Economics.

Investigators got another opportunity in 2007, when daylight time nationwide began three weeks earlier, on the second Sunday in March, and ended one week later in the fall. California Energy Commission resource economist Adrienne Kandel and her colleagues discovered that extending daylight time had little to no effect on energy use in the state. The observed drop in energy use of 0.2 percent fell within the statistical margin of error of 1.5 percent.

Not all recent analyses suggest that daylight saving is counterproductive. Instead of studying the impact daylight saving changes had on just one state, senior analyst Jeff Dowd and his colleagues at the U.S. Department of Energy investigated what effect it might have on national energy consumption, looking at 67 electric utilities across the country.

In their October 2008 report to Congress, they conclude that the four-week extension of daylight time saved about 0.5 percent of the nation’s electricity per day, or 1.3 trillion watt-hours in total. That amount could power 100,000 households for a year. The study did not just look at residential electricity use but commercial use as well, Dowd says.

The disparities between regional and national results could reflect climate differences between states. “The effect we saw could be even worse in Florida, where air conditioning is used heavily,” Kotchen suggests.

If time shifting turns out to be an energy waster, should the sun set on daylight saving? Certainly that would please farmers, who have long opposed it for how it disrupts their schedules. The chances, though, appear nil. “I’m skeptical we could change daylight saving time on a national level, because we’ve become accustomed to it,” Kotchen says, adding that “we might want to consider it for other costs or benefits it could have.” Retailers, especially those involved with sports and recreation, have historically argued hardest for extending daylight time. Representatives of the golf industry, for instance, told Congress in 1986 that an extra month of daylight saving was worth up to $400 million annually in extra sales and fees.

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